- Create TemplatePage with add form (category/tier/amount), items table, and empty state
- Add /template route to App.tsx with TemplatePage component
- Add Template nav item to sidebar (between Categories and Settings)
- Add template and nav.template i18n keys for EN and DE
- Fix unused import in useTemplate hook
- Add ItemTier type and TemplateItem/TemplateDetail interfaces to api.ts
- Add item_tier field to BudgetItem interface
- Add template API object with get/updateName/addItem/updateItem/deleteItem/reorder
- Add generate function to budgets API object
- Create useTemplate hook with CRUD operations and reorder logic
